Method for cleaning aluminum employing phosphine oxides

ABSTRACT

A METHOD FOR CLEANING ALUMINUM BY CONTACTING SAID METAL WITH AN AQUEOUS SOLUTION OF A PHOSPHINE OXIDE.

United States Patent 3,681,140 METHOD FOR CLEANING ALUMINUM EMPLOYING PHOSPHINE OXIDES Ronald H. Carlson, Lewiston, N.Y., assignor to Hooker Chemical Corporation, Niagara Falls, NY. No Drawing. Filed Mar. 30, 1970, Ser. No. 23,966 Int. Cl. 023g 1/18, 1/22; C231? 3/02 U.S. Cl. 134-2 11 Claims ABSTRACT OF THE DISCLOSURE A method for cleaning aluminum by contacting said metal with an aqueous solution of a phosphine oxide.

BACKGROUND OF THE INVENTION Due to the significant increase in the use of aluminum in various containers and in automobile engines, improved methods for cleaning aluminum are desired. A major problem in using aqueous baths, in particular, caustic soda baths, for aluminum etching is the tendency to convert the dissolved aluminum (sodium aluminate) into insoluble hydrous aluminum oxides which retard etching and brightening efliciency by forming a hard, tightly adherent scale on the etched tanks, heating coils and on the aluminum surface being etched. It has been found that the use of a phosphine oxide additive serves to retard scale formation thereby extending the bath life and producing a brighter etched aluminum surface. It has also been found that said phosphine oxide additive accelerates etch rate, and furthermore imparts a protective anti-corrosion film on the resulting etched surface.

It is an object of this invention to provide an improved agent for use in aluminum etching, in particular, in caustic aluminum etching.

SUMMARY OF THE INVENTION A method for cleaning aluminum metal is described. The composition employed is generally an aqueous composition containing a phosphine oxide. This agent can be used with or without other sequestering agents.

DESCRIPTION OF PREFERRED EMBODIMENTS The invention is concerned with a method of cleaning aluminum metal comprising contacting said metal with an aqueous solution of a phosphine oxide of the formula wherein R is an alkylene group of from 1 to 3 carbon atoms, and Z and Z' are independently selected from the group consisting of hydroxyl, alkyl groups of from 1 to 3 carbon atoms, and alkanol groups of from 1 to 3 carbon atoms.

The use of the following compounds as metal cleaning agents is for example, within the scope of this invention:

bis (hydroxymethyl) methylphosphine oxide, bis(hydroxymethyhphosphonie acid;

bis (hydroxymethyl) 3-hydroxypropylphosphine oxide; bis(hydroxymethyl) l-hydroxypropylphosphine oxide; bis (hydroxymethyl) 2-hydroxypropylphosphine oxide; bis(hydroxymethyl)propylphosphine oxide;

bis (hydroxymethyl) Z-hydroxyethylphosphine oxide; bis(hydroxymethyl) l-hydroxyethylphosphine oxide; bis(Z-hydroxyethyl)hydroxymethylphosphine oxide; bis-(l-hydroxyethly) hydroxymethylphosphine oxide;

hydroxymethyl-Z-hydroxyethylphosphinic acid; hydroxymethyl-l-hydroxyethylphosphinic acid; hydroxymethyl-2-hydroxyethylethylphosphine oxide; hydroxymethyl-1-hydroxyethylethylphosphine oxide; bis(3-hydroxypropyl)hydroxymethylphosphine oxide; bis( l-hydroxypropyl)hydroxymethylphosphine oxide; bis(Z-hydroxypropyl)hydroxymethylphosphine oxide; hydroxymethyl-Z-hydroxyethylphosphinic acid; hydroxymethyl-l-hydroxyethylphosphinic acid; hydroxymethyl-3-hydroxypropylethylphosphine oxide; hydroxymethyl-1-hydroxypropylethylphosphine oxide; hydroxymethyl-2-hydroxypropylethylphosphine oxide; bis(Z-hydroxymethyl)phosphinic acid; bis(2-hydroxyethyl)-3-hydroxypropylphosphine oxide; bis(2-hydroxyethyl) ethylphosphine oxide; bis(2-hydroxymethyl)methylphosphine oxide; tris(hydroxymethyl)phosphine oxide; 2-hydroxyethylmethylpropylphosphine oxide; 2-hydroxyethylmethylphosphinic acid; bis(Z-hydroxyethyl)propylphosphine oxide; bis (propyl) 2-hydroxyethylphosphine oxide; Z-hydroxyethylmethyl-3-hydroxypropylphosphine oxide; 2-hydroxyethylpropyl-3-hydroxypropylphosphine oxide; 3-hydroxypropylhydroxymethyl-Z-hydroxyethyl phosphine oxide; bis(B-hydroxypropyl) hydroxymethyl phosphine oxide; 2-hydroxypropylhydroxymethylethylphosphine oxide; 3-hydroxypropylhydroxymethylethylphosphine oxide; bis(Z-hydroxyethyl)-2-hydroxypropylphosphine oxide; 2-hydroxypropyl 2-hydroxyethylethylphosphine oxide; 2-hydroxypropyl-2-hydroxyethylpropylphosphine oxide; hydroxymethylpropylphosphinic acid; hydroxymethylmethyl-2-hydroxyethylphosphine oxide; bis(methyl)hydroxymethylphosphine oxide; hydroxymethylmethylethylphosphine oxide; bis (hydroxymethyl) ethylphosphine oxide; hydroxymethylethyl-3-hydroxypropylphosphine oxide; hydroxymethylethylphosphinic acid; bis(ethyl)hydroxymethylphosphine oxide; hydroxymethylpropyl-3-hydroxypropylphosphine oxide; hydroxymethylpropylphosphinic acid; hydroxymethylethylmethylphosphine oxide; bis(propyl)hydroxymethylphosphine oxide; hydroxymethylpropyl-Z-hydroxypropylphosphine oxide; hydroxymethylethyl-l-hydroxypropylphosphine oxide; tris(2-hydroxyethyl)phosphine oxide; tris 1-hydroxyethyl)phosphine oxide; bis(Z-hydroxyethyD- l-hydroxypropylphosphine oxide; bis(2-hydroxyethyl)phosphinic acid; bis (Z-hydroxyethyl) propylphosphine oxide; hydroxymethylphosphonic acid; l-hydroxyethylphosphonic acid; 2-hydroxyethylphosphonic acid; l-hydroxypropylphosphonic acid; Z-hydroxypropylphosphonic acid;

and the like.

Preferred embodiment is when Z and Z are alkanol groups of from 1 to 3 carbon atoms. Most preferred embodiment is THPO, i.e., tris.(hydroxymethy1)phosphine oxide. In subsequent description, THPO will be used because it is the most preferred embodiment. However, any of the other compounds mentioned above and falling within the generic formula, may be employed.

U.S. Patent 3,477,953 discloses the use of THPO when used as a sequestrant in a metal cleaning bath (e.g. derusting of ferrous metals). Although this patent mentions the aforementioned use, there is no description of its use in aluminum etching. The use of THPO in aluminum etching is not a typical sequestrant use since its function is not so much to prevent metal precipitation as in the usual metal cleaning bath, but to impart other desirable properties to the bath and to the etched piece of aluminum. These properties are an enhanced etch rate, longer lived etch bath, control of sludge and scale formation, increased brightness and corrosion resistance of etched surface. These aspects are further described in the working examples below.

The composition employed in this invention is an aqueous composition containing a phosphine oxide of the aforementioned generic formula, in the amount of about 0.001 to about 10% by weight, preferably 0.01 to 10% by weight and even more preferably 0.05 to by weight of the solution. A plurality of phosphine oxides may also be used. Other compounds may be used in conjunction with the phosphine oxide in order to improve the desired effect. Such additional compounds are gluconic acid or its water soluble salts.

It is preferred that the aqueous solution be caustic, such as in the range of from about 2 to about 20% by weight of NaOH and display a pH of greater than 12.

Operating temperature of the composition employed in this invention may range from about 15 to about 100 degrees centigrade. Preferred operating temperature may range from about 60 to about 90 degrees centigrade.

Having described the invention in general, below are further descriptions of the invention so that one of ordinary skill in the art may operate the invention.

Example 1 (1) amount of aluminum etched (removed) from panel surface (2) brightness of aluminum after etching (3) appearance of etch solution after treatment (4) effect of aging upon efficiency of etch solution ,(5) corrosion resistance of etched aluminum Preweighed, degreased 3" x 6" aluminum panels were completely immersed for 30 seconds in the afore'mem tioned solutions maintained at about 70 C., after which they were water rinsed, toweled dry and reweighed. The relative brightness of each panel was then measured by a photovolt reflection meter appropriately standardized. The following results were observed:

Relative Al Wt. perbrightness 1 cent Al Etch solution after etch removed THPO 39 0. 71 Gluconic acid 36 0. 80 Caustic 27 0. 94

1 The higher the number the brighter the Al surface. The data show that THPO removes less Al in producing a brighter surface than gluconic acid or caustic etch solutions.

Example 2 Degreased 3" x 6" aluminum panels were immersed for 10 seconds in each solution of Example 1. The following results were observed:

Relative Al Wt. perbrlghtness 1 cent Al Etch solution after etch removed Caustic 49 O. 28

'4 Example 3 An examination of the etch solutions following the two experiments described in Examples 1 and 2 showed:

Etch solution Color Odor Precipitate THPO Colorless None None. Gluconic Yellow Considerable Do. Caustic Colorless... None Yes.

1 Sugar acid fermentation products.

The etch solutions described in Examples 1-3 were aged at room temperature for 30 days and then re-evaluated by immersing 3" x 6" aluminum panels for 10 seconds. The following data show the greater long term stability of the THPO solution over the gluconic acid solution as evidenced by its superior etching activity after aging.

Etch Solution Reaction of Al panel to aged etch solution at 70 C.

THPO No reaction. Gluconic acid Immediate effervescene (usual etching activity.

Example 5 In another experiment to measure the relative stability of THPO and gluocnic acid against oxidative decomposition in an aqueous medium, 0.1% by weight of each compound was dissolved in 3% by weight H 0 containing 3 parts per million of dissolved iron as decomposition catalyst. The pH of each solution was adjusted to 8 and each solution was heated at C. until essentially complete H 0 decomposition took place. The relative iron sequesting power and hence the stability of each compound in the oxidizing medium was measured as a function of the time required to effect essentially complete H 0 decomposition (i.e., The more stable the iron sequestrant the more stable the H 0 solution). The following data show the markedly greater stability of THPO over gluconic acid in an oxidizing H 0 medium:

Sequestrant: Time required for H 0 decomposition THPO, hrs. 3% Gluconic acid, minutes 5 Example 6 Etched pieces of aluminum prepared in the manner of Examples 1 and 2 above were exposed to the laboratory atmosphere for approximately 18 months. Listed below are the results observed after this period of time.

Relative Al Relative Al brightness imbrightness 18 mediately after months after Etch solution etch etch Example 7 Another set of aluminum etching experiments was carried out with etch conditions set so as to simulate a typical commercial system.

(a) Etch bath compositions: 1 liter of aqueous solution containing 29.9 g. of caustic (3.0% bath weight). The additive baths contained 0.9 g. (3.0% caustic weight) of THPO or sodium gluconate.

(b) Apparatus: 2 liter stainless steel beaker equipped with copper heating coils and a Fahrenheit thermometer.

(c) Procedure: Weighed degrcased aluminum panels were immersed in each of the 3 etch baths (THPO, gluconate, caustic alone) until the desired amount of aluminum had reacted. Each bath was maintained at 180 F. by steam passing through the copper heating coils. The volume of each bath was maintained at 1 liter by addition of distilled water; no additional caustic or additive was introduced at any time during the etching experiment. Etch time was measured from initial placement of the first panel into the bath until the desired amount of aluminum had reacted. Test panels were weighed before and after etching to determine the amount of aluminum reacted. Etch rate was calculated by dividing the weight of aluminum reacted (in grams) by total etch time (minutes). The heating coils and stainless steel beakers were weighed before and after etching to determine the amount of adherent scale. The precipitated sludge in the bottom of each beaker was collected by filtration and dried and weighed. The formed sludge was judged as to its case of removal (still wet) from the beaker and its ease of removal (after drying) from the heating coils and walls of the beaker. The total weight of sludge and scale formed in each experiment was calculated from the weight of dried sludge removed from the bottom of the beaker plus the amount of scale adhered to the heating coils and beaker walls.

In this set of experiments a standard of approximately 18 g. of removed aluminum was used. Data are presented in the following table.

ALUMINUM ETCHING Sludge and scale The data show addition of THPO to a caustic etch bath (at a level of 0.9% bath weight) to reduce sludge formation by approximately 50% and to accelerate etch rate by 100%. The sludge and scale formed in the presence of THPO is softer and more easily removed than that formed in the absence of additive. Gluconate additive effects slightly less sludge formation than does THPO, with ease of sludge and scale removal being judged about equal with the two additives. The addition of gluconate however reduces etch rate by a considerable amount, efiecting an etch rate of less than 30% that experienced with THPO.

It is understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetwe'en.

6 In the claims: 1. A method for cleaning aluminum metal comprising contacting said metal with an aqueous caustic alkali solution of a phosphineoxide of the formula wherein R is an alkylene group of from 1 to 3 carbon atoms, and Z and Z are independently selected from the group consisting of hydroxyl, al-kyl groups of from 1 to 3 carbon atoms, and alkanol groups of from 1 to 3 carbon atoms.

2. The method of claim 1 wherein R is a methylene group and Z and Z are alkanol groups of from 1 to 3 carbon atoms.

3. The method of claim 1 wherein the phosphine oxide is tris(hydroxymethyl)phosphine oxide.

4. The method of claim 1 wherein R is a methylene group.

5. The method of claim 1 wherein Z is an alkanol of from 1 to 3 carbon atoms.

6. The method of claim 1 wherein Z is an alkanol of from 1 to 3 carbon atoms.

7. The method of claim 1 wherein the pH of the solution is greater than 12.0.

8. The method of claim 1 wherein the aqueous solution is maintained at a temperature from about 15 degrees centigrade to about degrees centigrade.

9. The method of claim 1 wherein the aqueous solution is maintained at a temperature from about 60 degrees centigrade to about 90 degrees centigrade.

10. The method of claim 1 wherein the phosphine oxide is present in an amount from about 0.001% to about 10% by weight of the solution.

11. The method of claim 1 wherein the phosphine oxide is present in an amount from about 0.05% to about 5% by weight.

References Cited UNITED STATES PATENTS 2,650,876 9/1953 Dvorkovitz et al. 25279.5 X

2,872,301 2/1959 Massengale et al. 134-2 X 3,477,953 11/ 1969 Carlson 252- 3,527,608 9/1970 Schlusser 134-2 FOREIGN PATENTS 913,343 12/1962 Great Britain 1342 OTHER REFERENCES Pfizer Advertisement; Chemical & Engineering News, Aug. 12, 1963, p. 13.

BARRY S. RICHMAN, Primary Examiner US. Cl. X.R.

323 UNITED STATES y E T OFFICE CERTIFICATE OF CORRECTION Patent No. 3,68l ,HlO- 1 Dated Auqust l, 1972 Inventor) Ronald H. Carlson It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

Column l last line hydroxyethly .shoul d read -hydrox yethyl ---=-1 Column 2, lines l3 and 16, "hydroxymethyl should read ---hyd-roxyethyl--- Column 3, line 73, "Blucom'c" should read --Glucon1'c---. 'Column I l ine l3, aodorless" should read ---odorless---; line 27, "No reaction. should read ---Immediate effervescence (usual etching activi'ty)-"--; lines 28 and 29, Immediate effervescene (usual etching activity) should read --No reaction.-; line 33, "gluocm'c" should read -glucon1'c---.

Column 5, line l6, 0.9% should read ---0.09%-- Signed and sealed this 2nd day of January 1973.

(SEAL) Attest:

EDWARD M.FLETC3HER,JR. ROBERT GOTT SCHALK- Attestlng Offlcer Commissioner of Patents 

